An expression is either of these:
- Integer literal: `0`, `1`, `3245`
-- String literal: `"hello, world"`, `""`, ```"this is
-a multiline
-string literal
-"```
+- String literal: `"hello, world"`, `""`,
+
+```
+"this is
+a multiline
+string literal
+"
+```
+
- Argument number: `$0`, `$1`, `$5`
- Function reference: `&function_name`
- Function call: `function_name(args)` or just `function_name`, where args is a comma-separated list of expressions.